The invention concerns expandable hose that reduces the hammering produced in hydraulic systems by pumps, with a tubular outer section of flexible material that has a fitting at each end and that loosely accommodates a tubular inner section of flexible material, leaving a hollow space between them, whereby one end of the inner section communicates with one of the fittings, allowing fluid to flow through it, whereas the other end is free and open, and whereby a fluid-conveying channel is left between the free end of the inner section and the other fitting. The use of expandable-hose sections of this type to decrease the noise of hammering in the power-steering systems of motor vehicles for example is known. The outer section is made from a material that is to some extent flexible. It can be constructed like a section provided with armor or reinforcement from a core, armor, and casing. When the pressure peaks characteristic of hammering occur, the outer section will expand accordingly to accommodate additional fluid and decelerate it. This action considerably reduces the hammering and the associated noise perceptible at the steering end.
An expandable hose of the aforesaid type is known from U.S. Pat. No. 3 323 305. The outer section has a fitting with a smooth inner surface all the way through it at the pump end and another at the steering end. Also communicating with the fitting at the pump end is a flexible inner section, the other end of which terminates free and open at a certain distance away from the fitting at the steering end of the outer section, leaving a fluid-conveying channel at that point. The free and open end of the inner section is surrounded by an open cap that decreases friction against the core deriving from motions on the part of the inner section inside the outer section. Since the inner section is, like the outer section, flexible, it can be employed in cramped situations in the vehicle. Since a tubular channel with the same dimensions and purpose as the channels at the ends surrounds the inner section, pressure waves will travel twice through the tubular channel and arrive phase-shifted in relation to other waves in the fluid-conveying channel, accomplishing both reduction and mutual cancellation. The tubular channel left around the total length of the inner section has an essentially solid wall and can accordingly be entered only from the fluid-conveying channel. There is no constriction between the fluid-conveying channel and the tubular channel. If the inner section has a radial perforation near where it is secured to the fitting at the pump end, fluid will be able to flow through the tubular channel from two ends on the principle of a bypass that pressure waves travel all the way through only once.
An expandable-hose section that reduces hammering is known from German OS 3 339 876. A flexible inner section is connected to the pump-end fitting in an outer section in this embodiment as well and extends essentially over the total length of the outer section, terminating in a free and open end somewhat upstream of the fitting at the other end. More or less at the midpoint of the length of the outer section there is a constriction between the inner and the outer section, creating two tubular channels in the hose. The inner section terminates free and open in this embodiment as well, and specifically in the second tubular channel. The inner section has constricting radial perforations for fluid to flow through only in the vicinity of the first tubular channel, and the fluid arrives in the second tubular channel through the constriction. This design is another example of a bypass, in that the fluid is provided with two different routes through the hose in order to decrease the noise deriving from the pressure waves in the second tubular channel by shifting their phases. The two tubular channels can also be considered fluid-conveying channels in that the fluid can flow through both.
U.S. Pat. No. 4 285 534 discloses an expandable hose with an outer section that has a constriction about halfway along its length. It has no inner section. The two fittings also have constrictions, creating a series of two fluid-conveying channels. Since there is a total of three constrictions in the series, a lot of pressure is undesirably lost.